In the aforementioned optical encoder, conventionally, for example, the signal track is formed so that an amount of penetrating light or an amount of reflected light, obtained by the light receiving elements from the light source via the signal track, is changed sinusoidally. In addition, the optical encoder includes a configuration in which each light receiving element is arranged at a position that is offset by ¼ of a pitch in the sinusoidal change in the amount of light. According to this configuration, signals being displaced by a 90° phase from each other can be obtained from the light receiving elements, and it becomes able to divide one period of the signal that is obtained from a pattern of the signal track into a plurality of segments (e.g., see patent document 1).
Furthermore, in an optical encoder having a plurality of diffraction gratings, in order to remove a harmonic distortion from an output signal, there is a type of the optical encoder in which the diffraction grating does not have a pattern with an interval between adjacent patterns being constant, and has a pattern with a predetermined phase difference with respect to a pattern of a reference phase and has a pattern having a phase difference that corresponds to a combination of a sum of each phase difference (e.g., see patent document 2).
Moreover, a technique of a Vernier encoder, which includes a main slit track having a predetermined wavenumber and a sub slit track having a wavenumber that is smaller than the predetermined wavenumber of the main slit track by a particular wavenumber, and generates a long period signal from a difference in an electrical angle between the aforementioned two tracks, is also suggested (e.g., see patent document 3).